This invention relates to a method of inspecting foreign substances in the form of, for example, gel which are contained in a photoresist (including a photosensitive resin) applied onto substrates, such as a semiconductor substrate, a printed circuit substrate, a connector substrate for electric connection, a nesa glass for liquid crystal display element, and various sensors. This invention further relates to an apparatus of inspecting foreign substances applying the aforementioned method.
Substrates, such as a semiconductor substrate, a printed circuit substrate, a connector substrate for electric connection, a nesa glass for liquid crystal display element, and various sensors, generally use a photoresist film to conduct exposure and development so that fine and accurate wiring patterns can be formed on the surface. However, since a photoresist film has a complicated molecular structure, when becoming insoluble through photoirradiation or conversely when becoming soluble to an alkali solution through photoirradiation, or when a photoresist film is affected by an abnormal charge or a partial heating during the manufacturing process of resin, gel substances may be occasionally created.
A silicon semiconductor substrate will be used as an example for this explanation. FIG. 5 is a schematic cross-sectional view showing a conventional apparatus used to inspect for foreign substances in a photoresist film. According to this conventional apparatus for inspecting for foreign substances in a photoresist film, a wafer 31 is mounted on a stage 32, and a laser beam is irradiated to the wafer 31 while moving the stage 32. In other words, when a measurement is conducted by using the foreign substance inspection apparatus comprising a laser irradiation instrument 29 and scattered light detectors 30, 30xe2x80x2, if a foreign substance is present in the photoresist film on the wafer 31, the laser beam is scattered by this foreign substance. In this way, the foreign substance in the wafer is detected and located by the scattered light detectors 30, 30xe2x80x2 (xe2x80x9cRinsing method for locating stain in a semiconductor waferxe2x80x9d, Yoshiichi Konishi, 1988).
However, the above-mentioned conventional method of inspecting foreign substances could not locate foreign substances in the form of, for example, gels which were created inside a photoresist film. This problem will be explained by using FIGS. 6(a) and 6(b). FIGS. 6(a) and 6(b) are partial cross-sectional views of a wafer showing a problem which is intended to be solved by this invention. With the above-mentioned conventional apparatus of inspecting foreign substances in a photoresist film, it was extremely difficult to detect, for example, a gel foreign substance 33 shown in FIG. 6(a) which was present inside a photoresist film 34. Furthermore, as shown in FIG. 6(b), when a gel foreign substance is present between patterns after the photoresist was developed, it is also difficult to detect the foreign substance because of a photoresist pattern 35 in the vicinity which reflects the light irregularly. In particular, when the gel foreign substance 33 is present between the patterns 35 as shown in FIG. 6(b), it causes a pattern failure.
It is an object of this invention to solve the above-mentioned problems in conventional systems by providing a method and an apparatus for inspecting for foreign substances in a photoresist film, to ensure detection of gel foreign substances which are present inside a photoresist film or between resist patterns.
In order to accomplish these and other objects and advantages, a method of inspecting foreign substances on a substrate surface of this invention comprises the steps of applying a photoresist on the surface of a substrate, exposing the photoresist, removing the exposed photoresist using a developing solution, irradiating a laser beam on the substrate surface which has the photoresist removed, and intercepting the scattered light to detect whether a foreign substances is present or not. According to this configuration, the photoresist is exposed, developed, and removed, so if a gel foreign substance is present inside a photoresist film or between patterns, this foreign substance is exposed. Therefore, it is possible to surely detect the presence of a foreign substance with a foreign substance inspection apparatus which has been used conventionally.
Next, an apparatus for inspecting for foreign substances on a substrate surface of this invention comprises a means for applying a photoresist on the surface of a substrate, a means for exposing the photoresist, a means for removing the exposed photoresist using a developing solution, and a means of irradiating a laser beam on the substrate surface which has the photoresist removed and detecting foreign substances by intercepting the scattered light. Accordingly, gel foreign substances which are present inside a resist film or between resist patterns can be detected surely and efficiently.
It is preferable in the above-mentioned method and apparatus of this invention that after the photoresist is removed with an alkali developing solution, ultraviolet rays are irradiated in an inactive atmosphere while heating at a temperature of from 150 to 250xc2x0 C . Thus, it is possible to generate a cross-linking reaction in a gel foreign substance and to prevent the gel foreign substance from changing its shape, so that the presence of a foreign substance can be detected surely even if an inspection takes place a long time after the photoresist was removed. In t his instance, the inactive atmosphere comprises, for example, an atmosphere of gaseous nitrogen.
Furthermore, it is preferable in this invention that the heating means comprises a hot plate, since a hot plate has excellent heating efficiency.
Also, it is preferable in this invention that after the photoresist is removed with an alkali developing solution, the substrate surface is subjected to an etching process and an ashing process, which is followed by washing the substrate. By exposing the photoresist and conducting the etching process using a gel foreign substance which remained through the development as a mask, gel foreign substances which are present in the photoresist film or between patterns can be detected.
In addition, it is preferable in this invention that the etching process comprises a method of etching a substrate surface with an average depth of 0.1 to 1 xcexcm using a reactive ion etching means. When it is etched with an average depth of 0.1 to 1 xcexcm, foreign substances can be detected accurately by irradiating a laser beam and intercepting its scattered light.
It is preferable in this invention that the ashing process comprises a method of heating a substrate surface at an average temperature of 200 to 300xc2x0 C. using a reactive ion etching means. Under this condition, gel foreign substances which remain between resist patterns can be ashed surely.
Furthermore, it is preferable in this invention that the method of applying a photoresist on a substrate comprises a rotary-coating (spin-coating) method. This is because this method enables a thin and an uniform coating of a photoresist. Furthermore, examples of photoresist include a resin which blocked a hydroxyl group of poly(p-vinylphenol) with t-butylester, a composition comprising a soluble polymer such as polyvinylalcohol (PVA) mixed with a photo-crosslinking agent such as ammonium dichromate, a multifunctional diazonium salt, a soluble bisazide compound, or a compound comprising a subring polyisoprene mixed with a bisazide compound (for example, 2,6-(4-azidebenzal)methycyclohexane), naphthoquinone diazide, and a novolak resin.
In addition, it is preferable in the above-mentioned invention that the method of removing a photoresist using a developing solution is performed by using at least one solution selected from the group comprising an inorganic alkali aqueous solution and tetramethyl ammonium hydroxide. These solutions are suitable for dissolving a resist.
Also, it is preferable that the method of washing a substrate after an ashing process is performed by using an aqueous solution containing sulfuric acid and hydrogen peroxide. The use of this aqueous solution enables surely removing ashed gel foreign substances.
It is preferable in this invention that the substrate comprises at least one substrate selected from the group comprising a semiconductor substrate, a printed circuit substrate, a connector substrate for electric connection, a nesa glass for liquid crystal display element, and various sensor substrates. These substrates can be suitably used as a substrate which is required to be patterned accurately and minutely using a resist.
According to the above-described method of this invention, the photoresist is exposed, developed, and then removed. As a result, if a gel foreign substance is present inside a photoresist film or between patterns, this foreign substance is exposed, so that its presence can be detected surely with an inspection apparatus of foreign substances which has been used conventionally.
Also, according to the apparatus of this invention, gel foreign substances which are present in a resist film or between resist patterns can be detected surely and efficiently.
According to the above-mentioned preferable method of inspecting foreign substances on a substrate surface of this invention, the method comprises the steps of applying a photoresist on the surface of a substrate, exposing the photoresist, removing the exposed photoresist using a developing solution, performing an etching process and an ashing process on the substrate surface, washing the substrate, irradiating a laser beam on the substrate surface after some time, and detecting foreign substances by intercepting the scattered light. In this way, gel foreign substances which are present inside a resist film or between resist patterns can be detected surely. In other words, by exposing the photoresist and conducting the etching process using a gel foreign substance which remained through the development as a mask, gel foreign substances which are present in the photoresist film or between patterns can be detected.
Next, according to the apparatus of inspecting foreign substances on a substrate surface of this invention, the apparatus comprises a means for applying a photoresist on the surface of a substrate, a means for exposing the photoresist, a means for removing the exposed photoresist using a developing solution, a means of etching and ashing the substrate surface, a means of washing the substrate, and a means of irradiating a semiconductor laser beam on the substrate surface and intercepting the scattered light for detecting foreign substances. In this way, gel foreign substances which are present inside a resist film or between resist patterns can be detected surely and efficiently.
This invention can be applied to various usages using a resist, for example, a semiconductor substrate, a printed circuit substrate, a connector substrate for electric connection, a nesa glass for liquid crystal display element, and various sensor substrates.